At the present time, various kinds of electronic coin validity-checking apparatus are in common use, for example employing one or more inductive sensing coils or transmit/receive coils at different positions spaced along a coin track along which a coin, inserted into the apparatus, travels. The sensing coils are connected to electronic processing circuitry in which the magnitude of a signal characteristic (i.e. frequency, amplitude or phase), which varies in dependence upon characteristics of the coin as the coin moves past the or each inductive sensor, is compared with predetermined values which are indicative of acceptable coins of one or more particular denominations. In this way, the validity of the test coin can be checked, and the coin rejected if it does not pass the appropriate tests.
The electronic circuitry when switched on is generally permanently energised from a power source. In many applications, continuous power consumption is unimportant. For example, when the validation circuitry is used in combination with a vending machine for dispensing hot drinks, the proportion of the average power consumed by the processing circuitry is negligible as compared with that required by the heater and control equipment in the vending machine. However, in certain uses of coin validity-checking apparatus such as in pay telephones which are supplied from relatively low power supplies or cigarette vending machines or parking meters supplied from batteries, the average power consumed by validation circuitry of the kind described is unacceptably high. In pay telephones in use in many countries throughout the world, various forms of mechanical coin validity-checking apparatus are still adopted at the present time and whilst it would be desirable to replace these mechanical systems with electronic apparatus to improve the integrity of the validation checks carried out on inserted coins, known electronic coin validity-checking apparatus are generally unable to comply with the requirement for the very low average power consumption (e.g. 2 mA at 5 volts).
In our British Pat. No. 1,483,192, there is disclosed electronic coin validity-checking apparatus which comprises a transmitter/receiver inductive arrival sensor operative to produce an output signal when an inserted coin passing between the coils along a coin passage is of an acceptable material. At a position further downstream the coin passage, the coin is optically tested to check its velocity, diameter etc. as disclosed in our U.K. Patent Specification No. 1,272,560, and if the coin passes both the initial inductive and subsequent optical tests, the coin is accepted through an acceptable gate into an acceptance passageway. The optical test involves the use of light sources with associated optical coin sensors such as photoelectric devices. If these optical sources are permanently energised, they have a particular expected life. Therefore, to extend the expected life of these sources, the light sources are switched on by the output signal from the inductive arrival sensor. The trend in recent years has been towards inductive and capacitive techniques for carrying out the desired measurements of coin characteristics in the examination region, but as mentioned above the total power consumption in known coin handling mechanisms is unacceptably high for certain applications.
In U.S. Pat. No. 3,738,469, various forms of apparatus are disclosed for examining coins in which each coin is firstly checked for size by a sensing switch of one form or another, and then a second test is performed by a measuring probe. The coin is accepted only if it passes both tests. The apparatus is continuously supplied with power but this is disadvantageous where the apparatus is dependent upon battery power. In order to reduce the power consumption, it is possible to utilise the diameter sensitive switch to switch-in and switch-out the current supply network. However, the switch is operated by the coin before the coin arrives in the examination region of the measuring probe so that, despite the measures taken, the current supply network is switched in slightly prematurely. Also, the diameter sensitive switch is set to be operated by contact of the coin edge as the coin passes the switch, whereas at the present time contactless measurements are to be preferred for several reasons including reliability. In addition, the switch arranged at a particular spacing from the coin track can detect coins of one size only and therefore is not suitable for multi-denomination use where only a single coin track is employed.